In this study, the term "sand" is used for unconsolidated sediment composed of sand-sized grains, and "sandstone" is used to describe its consolidated equivalent. Sand-sized grains, which have been derived from preexisting rocks, will be described herein as detrital. Sand and sandstones are described as framework- or matrix-supported based on the amount of matrix, "matrix" being defined as detrital material with an average diameter of <30 µm (Dott, 1964). Framework-supported rocks contain <15% matrix, whereas matrix-supported rocks have >15%. The sandstones and sands were further divided on the grounds of their relative proportions of feldspar and lithic and bioclastic particles (Table T3; Pl. P1, figs. 1-6). In the text where the terms abundant, common, rare, and trace are used to describe relative proportions of constituents of sands/sandstones, they are based on the following: abundant = 51%-100%, common = 11%-50%, rare = 1%-10%, and trace = <1%.
Detrital quartz grains are either present in only trace amounts or absent in the sand and sandstones. Grains range from rounded to angular and strained to unstrained. They are colorless and commonly include trails of tiny fluid inclusions. Quartz also occurs as intergrowths with feldspar in granitic grains and rarely as phenocrysts within felsic volcanics. Polycrystalline quartz aggregates (made up of quartz grains <0.0625 mm) and vein quartz are observed in a few samples.
Detrital feldspars occur in all samples. Except for those grains that show multiple twinning or zoning, it is generally not possible to distinguish between plagioclase and alkali feldspar microscopically. Staining tests with sodium cobaltinitrite indicated the presence of only trace amounts of potassium feldspar. Therefore, the feldspars are separated into (1) untwinned feldspar and (2) twinned and zoned feldspar (Pl. P2, fig. 4). The latter is assumed to be plagioclase, as no cross-hatch twinning characteristic of microcline is observed. Some feldspar grains are fresh and unaltered, whereas others are partially replaced by secondary minerals, including white mica, albite, calcite, and clay minerals. Some of the feldspar shows myrmekitic intergrowths of plagioclase and quartz (e.g., Sample 180-1115C-26R-1, 8-9 cm). Apatite prisms occur rarely in feldspar grains (e.g., Sample 180-1108B-23R-3, 35-36.5 cm).
Detrital biotite is present in the majority of samples. It occurs as mostly brown and green cleavage flakes. In addition to occurring as discrete detrital grains, it is observed as phenocrysts within volcanics, intergrown with quartz and feldspar in granitic fragments, and as aligned plates in schist grains. Secondary calcite growth along biotite cleavage is common (Pl. P2, fig. 2). Smaller, less common muscovite laths occur as discrete detrital grains and as aligned laths in the schist grains. Pyrite blebs occur along the cleavage planes of some muscovite grains (e.g., Samples 180-1109C-24X-CC, 18-20 cm, and 180-1108B-5R-CC, 6-8 cm).
Clinopyroxene and hornblende grains, in addition to being constituent minerals of volcanic lithic grains, occur as discrete subhedral to euhedral grains. Under plane-polarized light the clinopyroxene is mostly colorless, whereas the hornblende grains are green or, less commonly, red/brown in color. Clinopyroxene identified is all calcic and is probably dominantly augite, although some diopside may be present (Cortesogno et al., this volume). Detrital grains composed entirely of aggregates of clinopyroxene or hornblende crystals are probably derived from glomeroporhyritic phenocrysts, observed within lithic volcanic detritus (e.g., Samples 180-1108B-27R-5, 61-63 cm, and 180-1115C-29R-1, 72-73 cm) (Pl. P2, fig. 3). Rarely, clinopyroxene grains have been altered to amphibole (Sample 180-1108B-27R-5, 61-63 cm). Grains of hornblende and clinopyroxene in some samples exhibit brown irregular iron oxide rims (e.g., Sample 180-1114A-28R-CC, 3-7 cm). Clinopyroxene grains are commonly twinned and zoned. Green hornblende forms phenocrysts within felsitic and colorless vitric volcanic fragments, whereas brown hornblende forms phenocrysts within the lathwork and brown vitric volcanic grains. Green hornblende is intergrown with feldspar and quartz in granitic fragments (e.g., Sample 180-1108B-30R-1, 42-44 cm). Actinolite is present in trace amounts (e.g., Samples 180-1108B-32R-2, 126-128 cm, and 180-1115C-29R-1, 72-73 cm) (Pl. P3, fig. 6).
Goethite concretions (Pl. P2, fig. 1) are numerous in Sample 180-1109D-44R-1, 6-8 cm, where they form 26.5% of the framework components. These were interpreted by Robertson et al. (2001) as bog iron ore. Rare detrital aggregates of prehnite and pumpellyite are present (e.g., Sample 180-1116A-6R-1, 9-11 cm). Trace amounts of detrital epidote and zircon grains are present, with the former occurring as clusters in some samples (e.g., Samples 180-1108B-36R-3, 52-56 cm, and 180-1116A-7R-CC, 25-27 cm). Trace amounts of chalcedony are present as fill within vugs of volcanic fragments or as detrital grains (Pl. P2, fig. 6). Olivine grains are sporadically present in trace amounts; although in Sample 180-1109C-24X-CC, 18-20 cm, they comprise 7% of the rock. Trace amounts of spinel grains are present but were not counted in any of the samples (e.g., Samples 180-1108B-3R-CC, 0-4 cm, and 30R-1, 42-44 cm). Trace to common amounts of chloritic detritus is present in many of the sandstones. Opaque minerals form minor constituents in most sandstone but were not characterized in detail. Authigenic pyrite is most common, with trace amounts of detrital chromite and magnetite also present. Pyrite occurs as framboids and disseminated grains. It is commonly associated with foraminifer tests, vitric volcanic fragments, carbonaceous detritus, and detrital mica grains. Dendritic magnetite growths are observed within dolerite clasts (Pl. P4, fig. 2).
Following Dickinson (1970), volcanic lithic grains are subdivided into vitric, felsitic, microlitic, and lathwork. In this study we further divided vitric (glass) fragments according to their color as viewed under plane-polarized light (ie., colorless [Pl. P5, fig. 1] or brown [including tan, brown, and black] [Pl. P5, figs. 2, 3]). The vitric category includes fragments of colorless pumice, colorless glass shards, pipe-vesicle and bubble-wall fragments, and tan, brown, and black glass of variable vesicularity. In some of the samples, the glass shows incipient devitrification. Zeolitized glassy fragments are rarely present (e.g., Sample 180-1118A-36R-3, 52-56 cm). Some brown vitric fragments are altered to palagonite. Calcite and chlorite are observed replacing both brown and colorless vitric fragments. Large colorless pumiceous vitric fragments contain phenocrysts of green hornblende, plagioclase, biotite, and, rarely, clinopyroxene (Pl. P2, fig. 5). Brown vitric fragments commonly contain sparse phenocrysts of plagioclase, red to brown hornblende, biotite, and, rarely, clinopyroxene. Rare relict fiamme (elongate, flattened pumice) and calcite amygdales are present in a few brown vitric grains.
Microlitic volcanic lithic fragments contain variable amounts of feldspar microlites that commonly show a trachytic texture. Microlitic fragments are further divided into hyalopilitic (glassy) or pilotaxitic (holocrystalline) according to the nature of their groundmass (Pl. P5, figs. 4-6). The hyalopilitic grains have been further divided according to glass color. Microlitic clasts are plagioclase-, rarely biotite-, hornblende-, and/or clinopyroxene-phyric.
Lathwork volcanic fragments are characterized by plagioclase laths with intersertal brown or colorless glass and/or, rarely, intergranular clinopyroxene (Pl. P4, figs. 1-4). The intersertal glass in some grains is chloritized. Some lathwork grains are plagioclase-, clinopyroxene-, and hornblende-phyric. The hornblende is commonly reddish to brown in color. Glomeroporhyritic clusters of clinopyroxene are present in a few lathwork grains. Plumose feldspar dominates some lathwork lithic fragments (Sample 180-1115C-30R-CC, 10-12 cm).
Felsitic volcanic fragments are mostly porphyritic with euhedral to subhedral feldspar and/or, rarely, quartz phenocrysts set in a microcrystalline groundmass of quartz and feldspar (Pl. P4, fig. 5). Phenocrysts of biotite and hornblende are commonly present. Feldspars are commonly replaced by white mica, albite, and/or calcite.
Schist and gneiss grains form quartz-feldspar aggregates with a foliation defined by aligned flakes of mica, rarely aligned hornblende prisms, and elongate quartz and feldspar crystals (Pl. P3, figs. 4, 5). The clasts are cut by rare epidote and chlorite veins (Pl. P3, fig. 3). Feldspar within some clasts is altered to albite; prehnite and pumpellyite are also present in some grains (e.g., Samples 180-1108B-14R-1, 97-99 cm). Large sand-sized quartz and feldspar crystals within the otherwise microcrystalline aggregates are interpreted as relict phenocrysts (Pl. P3, fig. 5). A continuous range of variation from felsitic volcanic fragments and metamorphosed felsic volcanics is present. Calcareous schist fragments initially reported by Taylor, Huchon, Klaus, et al. (1999) are reinterpreted here as detrital mica grains with authigenic calcite growths along cleavage planes (Pl. P2, fig. 2).
Serpentinite grains are distinctive because of their green-yellow and black lattice texture and high degree of roundness (Pl. P3, fig. 2). These grains commonly have abundant internal opaque mineral grains and rare relict olivine and pyroxene crystals (e.g., Samples 180-1108B-3R-CC, 0-4 cm, and 30R-1, 42-44 cm) (Pl. P3, fig. 1). Brown iron oxide rims occur around a few of the serpentinite grains. Serpentinite grains have been included in the metamorphic rock fragments category, although they probably formed under temperature conditions lower than those of the schist and gneiss fragments.
Plutonic fragments are uncommon. They are mainly rounded to angular grains of intergrown anhedral feldspar and quartz derived from granitic rocks (Pl. P4, fig. 6), although grains composed almost entirely of feldspar may have been derived from less silicic rocks. A number of grains contain hornblende and biotite. Graphic textures are observed in few of the fragments.
Matrix is principally composed of tiny detrital fragments of volcanic glass, feldspar, mica, and clay minerals (including chlorite, illite, smectite, and kaolinite). Sparry calcite is the most common cement, but chlorite, smectite, and other clay minerals are also contributors. Abundant microfossils (i.e., planktonic foraminifers, coccoliths, siliceous sponge spicules, and radiolarians) are present in the matrix.
Two categories of carbonate detrital grains were counted: (1) skeletal grains, which included fragments of planktonic and benthic foraminifers, coralline algae, shell, bryozoans, echinoderm plates, bivalves, and gastropods; and (2) carbonate aggregates, which include micritic detrital aggregates of uncertain origin. Recrystallized limestone fragments are included in the second category (e.g., Sample 180-1108B-24R-3, 39-41 cm).
Detrital carbonaceous fragments range from brown to black in color. Disseminated and framboidal pyrite of inferred authigenic origin occurs within the carbonaceous fragments.